Silicon oxide is a dielectric material that is widely employed in the fabrication of semiconductor devices. Silicon oxide may be formed in a number of ways. In one approach, silicon oxide may be thermally grown from an underlying silicon material through exposure to oxidizing agents.
Alternatively, silicon oxide may be formed through the process of chemical vapor deposition (CVD). One example of such a CVD reaction involves the reaction of ozone (O3) and tetraethylorthosilane Si(OCH2CH3)4 (TEOS) gases at elevated temperatures, resulting in the deposition of silicon oxide as a solid material. In a typical conventional TEOS O3—O2 CVD process for forming silicon oxide, silicon-containing precursor materials and oxidant are flowed into the deposition chamber simultaneous with the application of heat. As a result of these conditions, silicon oxide layers are rapidly formed.
One particularly important use for silicon oxide is in the formation of shallow trench isolation (STI) structures between active devices of an integrated circuit. FIG. 1A shows a cross-sectional view of the typical starting point for formation of an STI structure. Mask 102 comprising silicon nitride layer 104 overlying pad oxide layer 105 is patterned over silicon substrate 106. Silicon in unmasked regions 108 is removed to form trenches 110. Silicon sidewalls 112 of trenches 110 are then exposed to an oxidizing ambient to form thermal oxide trench liner 114.
As shown in FIG. 1B, conventionally the shallow trench isolation structure is formed by depositing silicon oxide over the entire surface, including over mask 102 and within trench 110. However, the thermally grown oxide 114 provides a relatively inactive surface that results in lower rates of oxide deposition within trench 110. The higher rate of deposition of oxide over silicon nitride layer 104 of the mask 102 may cause greater accumulation of oxide material outside of trench 110, resulting in the possible formation of voids 116 within trench 110. Voids 116 can degrade the dielectric properties of the STI structure that is ultimately formed.
Accordingly, new and improved processes for forming uniform, high quality layers of silicon oxide are valuable.